Technical Field
The present disclosure relates generally to differential feedback amplifiers. More particularly, the present disclosure relates to differential feedback amplifiers having multiple feedback paths. Specifically, the present disclosure relates to feedback paths incorporating cross-coupled switches for differential feedback amplifiers.
Background Information
Data transmission often requires the use of an amplifier to amplify a signal. One exemplary data transmission utilizes differential signaling. Differential signaling is a method for electrically transmitting information using two complementary signals. Differential signaling sends a single electrical signal as a differential pair of signals, each in its own conductor (a positive signal (+) and a negative signal (−)). Differential signaling is frequently used in audio, data transmission, and telephone systems, amongst others. Differential signaling is beneficial because of its resistance to external noise sources.
During the differential signaling process, a differential amplifier is often used to amplify the differential pair of signals. Differential amplifiers are considered beneficial because they can increase immunity to external noise, increase output voltage swing for a given voltage rail, enable low-voltage systems, are easily implemented in integrated circuits, and reduce even-order harmonics, amongst others.
Some differential amplifiers have feedback paths or feedback networks coupling the amplifier's output back to its input. These may be referred to as a differential feedback amplifier. Compared to open loop amplifiers, feedback amplifiers inherently have a comparatively low impedance connection (when compared to the impedance seen from the output to input of a non-feedback amplifier) from their output to input, which is the feedback path. Feedback is very useful because it can stabilize and precisely set the overall performance of a potentially unstable and imprecise high gain, open loop amplifier. However, benefits aside, there are some known drawbacks. Feedback paths may reduce off-state isolation because the feedback path is a connection through which an extraneous and undesired system signal may travel. This feedback path connection provides an electrical pathway around the amplifier circuitry that reduces both the forward and reverse isolation of the circuit compared to conventional differential amplifier topologies that that have no feedback path.
In many electrical systems, high isolation is desirable when the amplifier is powered down (off-state), and the feedback paths of a differential feedback amplifier can severely degrade this. To increase off-state isolation, switches can be added in series, but these negatively impact the performance of the amplifier when it is operating normally. Some conventional amplifiers utilizes switches along the feedback path or switches near the feedback systems/circuitry to enable selective control of the feedback signal, but again these negatively impact the performance of the amplifier when it is operating normally (i.e., on-state).